In line with the realization of miniaturization and weight reduction in electronic devices and the generalization of the use of portable electronic devices, research into secondary batteries having high energy density, as power sources of such electronic devices, has been actively conducted.
The secondary batteries may include nickel-cadmium secondary batteries, nickel-metal hydride secondary batteries, nickel-hydrogen secondary batteries, and lithium secondary batteries, and in particular, among these batteries, research into lithium secondary batteries, which not only have a discharge voltage two or more times higher than a typical battery using an alkaline aqueous solution, but also have high energy density per unit weight and is capable of rapid charging, has emerged.
The lithium secondary battery is composed of a cathode formed of a lithium metal oxide, an anode formed of a carbon material or a lithium alloy, and an electrolyte formed of a lithium salt and an organic solvent.
In this case, since the organic solvent is easily volatized and has high flammability, short circuit and fire due to internal heat during overcharge and overdischarge may occur. Thus, high-temperature safety of the lithium secondary battery may be reduced.
Therefore, research into developing an electrolyte capable of improving cycle life and high-temperature lifespan of the battery has been variously attempted.